Physical Metallurgy - Lesson 2
Plastic Deformation of Metals
Page 1: Introduction to Plastic Deformation
Definition and overview of the concept of plastic deformation in metals.
Page 2: Definition of Deformation
Deformation: A change in dimension or shape of a material brought about by an applied stress.
Page 3: Deformation in Metals
Illustrates the significance and impact of deformation in metals.
Page 4: Deformation in Structures
Discusses the implications of deformation in structural applications.
Page 5: Deformation in Metal Processing
Examination of how deformation influences various metal processing techniques.
Page 6: Types of Deformation
Elastic Deformation
Plastic Deformation
Page 7: Elastic Deformation
Characteristics: Refers to ‘temporary deformation’ where the material returns to its original shape after the load is removed.
Page 8: Plastic Deformation
Characteristics: Refers to ‘permanent deformation’ where the material does not return to its original shape after loading.
Page 9: Quantitative Measure of Deformation
Deformation measured as strain: Strain (e) = ΔL / Li x 100%, where ΔL = Lf - Li and Li = initial length.
Page 10: Engineering vs True Stress and Strain
Engineering Stress (σ): F / A
Engineering Strain (ε): ΔL / L0
True Stress (στ): F / Ainst
True Strain (ε): dL / L
Page 11: Relationships between Engineering and True Measures
Engineering strain to true strain: ε = ln(e+1)
Engineering stress to true stress: σ = σ (e+1)
Page 12: Stress-Strain Curve
Depicts the mechanical properties of metals as obtained from the Tension Test.
The curve reflects the load-elongation characteristics of the material.
Page 13: Tensile Test Setup
Components involved: Load cell, extensometer, specimen, and moving crosshead.
Page 14: Stress-Strain Curve Description
Includes critical points such as yield point, ultimate stress, and the failed point of the curve.
Page 15: Elements of the Stress-Strain Curve
Distinction between elastic deformation and plastic deformation through stress (σ) and strain (ε) ranges.
Page 16: Toughness and its Relation to the Curve
Toughness: Energy needed to break a unit volume of material, represented by the area under the stress-strain curve.
Metals exhibit larger toughness compared to ceramics and certain polymers.
Page 17: Data from Stress-Strain Curve
Identifies ultimate stress, yield stress, and their positions within elastic and plastic regions of the curve.
Page 18: Plastic Deformation in Single Crystals
Examines phenomena in materials such as olivine post deformation analysis (N. Christensen, 1995).
Page 19: Slip Lines in Metals
Visual depiction of straight slip lines in copper post deformation.
Page 20: Shearing Stress in Crystals
Illustrates the sinusoidal relationship of displacement under shearing forces.
Highlights that actual strength is significantly lesser than theoretical strength due to the presence of dislocations.
Page 21: Yield Strength Discrepancy
Explains that actual yield strength is lower than theoretical strength due to dislocations, which facilitate slip in the crystals.
Page 22: Perfect Materials: Whiskers
Discusses the ideal properties and strength of whiskers made of materials like iron.
Page 23: Formation of Dislocations
Sources of Dislocations: Includes solidification issues and applied stress conditions (homogenous and heterogeneous).
Page 24: Burger's Vector
Defines dislocation distortion in lattice structures, described with magnitude and direction.
Page 25: Burger's Circuit
Visual representation of Burgers circuit illustrating dislocation types (screw dislocation).
Page 26: Stress Field Interactions
Discusses stress fields in dislocations and their environmental interactions.
Page 27: Dislocation Multiplication
Illustrates the generation of dislocation loops and Frank-Read sources for dislocation multiplication.
Page 28: Frank-Read Source Overview
A visual representation showcasing the mechanism of dislocation generation and multiplication.
Page 29: Slip in Perfect Crystals
Contrast views showcasing the state of crystals before and after slip.
Page 30: Slip Plane in Perfect Crystals
Highlights the designated slip planes where deformation occurs preferentially.
Page 31: Slip Steps in Crystalline Structures
Details the steps and mechanics of lattice slip during deformation.
Page 32: Challenges of Slip in Perfect Crystals
Slip is difficult due to the requirement to break bonds simultaneously across the lattice.
Page 33: Slip in Defective Crystals
Easier slip occurs as atoms only need to break bonds incrementally.
Page 34: Models of Dislocation Movement
Overview of how dislocations move and the directionality of their motion.
Page 35: Conservative vs Non-Conservative Motion
Differentiates between glide (conservative) and climb (non-conservative) dislocation movements.
Page 36: Non-Conservative Motion Description
Types of non-conservative motions including climb and associated conditions.
Page 37: Types of Non-Conservative Motion
Detailed breakdown of climb and cross slip in dislocation movements.
Page 38: Cross Slip Dynamics
Mechanics of screw dislocation movement across slip planes.
Page 39: Slip along Atomic Planes
Describes preferential slip along high-density planes resulting in minimum atomic displacement.
Page 40: Slip Systems in Crystalline Metals
Summary table listing crystal structures, slip planes/directions, and examples of metals.
Page 41: Causes of Slip
Slip occurs uniquely under shear stress specifically resolved in the slip plane and direction.
Page 42: Resolved Shear Stress Calculation
Formula and application to derive resolved shear stress necessary for dislocation movement.
Page 43: Critical Resolved Shear Stress (CRSS)
Defines CRSS as the threshold stress needed for plastic deformation.
Page 44: CRSS Values in Metals
Comparative overview of CRSS for different metals indicating capacities for deformation.
Page 45: Twinning Mechanism
Discussion of twinning in metals, particularly in BCC or HCP structures, under specific conditions.
Page 46: Twin Characteristics in Microstructure
Highlights typical features of mechanical and annealing twins in microstructural analysis.
Page 47: Slip vs. Twinning Comparison
Differences between slip and twinning, focusing on lattice reorientation and atomic spacing.
Page 48: Slip vs. Twinning Visuals
Illustrative comparison of slip and twinning mechanisms in a crystallographic context.
Page 49: Sample Problem Overview
Presents a brief case study with a steel bar to demonstrate calculation of stress and strain.
Page 50: Calculation Setup
Initial and final state data for problem-solving on fracture stress and strain.
Page 51: Engineering and True Stress Calculation
Engaging in calculations to derive the appropriate fracture stress and strains from the data provided.